Have a flat roof (standard roofing felt) that meets up with a sloping slated one. The flat roof is angled slightly so the slate roof takes all the rain water from it.
The joint between the two is covered in lead.
Even when new, I'd had an occasional problem with a leak which seems to be from there - but can't be sure as there is plasterboard covering it in the inside. But when it does leak, water seems to run down one of the joists for the sloping roof (where you can see them, some way down from that join)
Now lead isn't going to provide a seal against driving rain, so just how should this joint be constructed?
I'd expect the felt to overlap the slate, and the lead just there to protect things?